The present invention concerns washed sand drying and handling plant. Traditionally, after sand has been washed, it is allowed to slide down a chute onto a conveyor belt which then transports the sand to a stockpile. This just-washed sand usually contains about 22-26% w/w moisture content. Thus, the sand is still quite wet and it must be dried to about 8-10% w/w moisture content before it can be transferred to another stockpile using loading shovels or dumpers. This method of drying and handling sand is time consuming, labour-intensive and costly. It is necessary to wait about 14 hours before the washed sand can actually be used. Therefore, if the stockpile of dried washed sand available for use is small, it would be necessary to wait 14 hours before any further stocks of dried washed sand would be available for use.
The specification of DE-A-33 08 540 discloses an apparatus for the dewatering and drying of, for example, the sand from the sludge liquor of a gravel washing plant. The apparatus comprises two sludge separating stages which each comprise a horizontally extending tank container which has a collecting trough at its bottom end, parallel to its longitudinal axis, in which trough a worm conveyor rotates. The trough opens into an elevator ending in the region of a sludge drying container, which elevator likewise has a worm conveyor, each horizontal tank container bearing, in the upper region of its shell, an inlet basin for the sludge flow and an overflow basin for the sludge flow having reduced proportion of sludge.
The present invention seeks to alleviate the disadvantages associated with the above.
The present invention accordingly provides a washed sand drying and handling plant comprising: apparatus for washing with water sand with water; apparatus for dewatering the washed sand; apparatus for transporting the washed sand from the dewatering apparatus to a vessel adapted for storing the dewatered sand and enabling the sand to dry by gravity, the sand being held in the vessel for a predetermined amount of time sufficient to allow the sand to dry to the desired level wherein each vessel includes an inner membrane through which the liquid from the washed sand in the vessels drains. Preferably, the plant includes means for collecting and recycling the drained liquid to the dewatering apparatus.
Conveniently, the plant includes a plurality of said vessels, whereby when a first vessel is full, sand from the dewatering apparatus is delivered to a second vessel and so on.
The present invention also includes a conveyor by means of which the sand is deliverable from the dewatering apparatus to the vessel, the conveyor being moveable through an arc, so that the conveyor can be moved through a predetermined angle when the first vessel is full, resulting in the conveyor being positioned over a mouth of the second vessel and the dewatered sand being delivered to the second vessel.
Conveniently, each vessel comprises a tank having a cone shaped lower section with the inner membrane forming an inner wall of the cone and having a multiplicity of apertures to allow liquid to drain into a space between the inner wall and an outer wall of the cone.
Preferably, the membrane is provided on a removable filter element mountable within the outer wall of the cone.
Advantageously, a water supply is provided in the space between the inner and outer walls of the cone. More advantageously, the or each vessel is provided with a detector to ascertain when it is full.
Ideally, a moisture probe is located at the base of the vessel for determining when the sand is at the required moisture level.
Conveniently, a door is provided at the base of the or each vessel and a conveyor is located between the door or doors of the vessel or vessels, with the or each door being openable.
Advantageously, an adjustable chute is provided at the head of the transporting apparatus to direct sand into a vessel.
The present invention also provides a vessel for holding wet sand, the vessel including an inner membrane through which the liquid from the washed sand in the vessel drains, the vessel further including a conical base, a complementary shaped filter within the base spaced from the walls of the base to provide a drainage space between the filter and the base, whereby sand deposited in the vessel dries by gravity and without the use of a heat source.
The invention will now be described more particularly with reference to the accompanying drawings in which are shown, two embodiments of plant according to the invention.